Summary of Significant Accounting Polices - Outstanding Potentially Dilutive Securities that are Anti-Dilutive (Details 6) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	2,407,844	1,880,053	7,661,010
Redeemable Convertible Preferred Stock
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)			6,292,369
Convertible preferred stock warrants
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)			205,020
Common stock warrants
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	242,779	62,505
Stock options
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	2,165,065	1,817,548	1,163,621